[lug] need cat5 wiring/"Dest host unreachable" help

John Karns jkarns at csd.net
Fri Oct 19 20:40:09 MDT 2001

I've encountered problems similar to what you describe when installing
cat-5 cable due to excessive cable length.

If the length of your patch cords (cables having the RJ-45 connectors on
them) exceeds 5 meters, that could be your problem.  Patch cords are
spec'd to have a maximum length of 5 meters.  I assume this is due to high
signal attenuation characteristics of the RJ-45 connectors.  For cables
exceeding 5 meters, you need to use a jack, which installs with a punch
tool.  That type of connector minimizes the attenuation.  Along those
lines, I would also check that the wire connections to the jacks are "well
pinched".  Even though a continuity check will reveal a good connection,
characteristics are quite different at 100 Mhz.  Finally, I would try
connecting the two floating pair.

On Thu, 18 Oct 2001, Michael J. Hammel said:

> I'm trying to wire my upstairs game room to my downstairs office with
> CAT5 cable.  The cable was already run when the house was built.  But
> the connections were mucked up.  So I'm trying to fix them.
> My office has a gateway connected to a hub with 3 other computers
> (including a laptop) hooked directly into the hub.  All that works
> fine.  I connected the CAT5 cable in the wall to an CAT5 jack and
> moved the cable that was running to the laptop from the hub into the
> wall.  Upstairs I used the same wiring combination on the jack (see
> below) and plugged another cable from that jack into my laptop.
> I get a link light on the laptops connector (external pcmcia type) and
> on the hub.  However, when I ping anyone on the downstairs net from
> the laptop upstairs (or reverse the direction) I get "Destination Host
> Unreachable". I think the wiring is correct.  But I can't ping anyone
> on opposite floors.
> I doubt the cable is over 100 meters in total length, so that
> shouldn't be the problem.  None of the cabled used to plug the laptop
> into the wall or the wall into the hub is a crossover cable, so that's
> the not the problem.
> Is the timeout for the ping expiring and making it look like the
> remote hosts can't be reached?  Should any of the transmit/receive
> wires be crossed?
> I used the T568B standards for the wiring and run in straight through.
> The wire from downstairs runs to a junction box where it is connected
> straight through to to the wire that runs to the wall in the game
> room.
> Anyone got any suggestions?  Some of the twists came out of the wires
> so I added them back in (I've heard that helps reduce noise).  But
> that didn't help.  The green/green-white pairs seem to provide link
> lights.  The orange/orange-white pairs seem to provide data.  Is that
> correct?  The blue/blue-white and brown/brown-white pairs are unused
> as far as I know. Those latter sets are currently unconnected.

John Karns                                        jkarns at csd.net

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